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x4+2012x2+2011x+2012
=(x4-x)+(2012x2+2012x+2012)
=x(x3-1)+2012(x2+x+1)
=x(x-1) (x2+x+1) + 2012 (x2+x+1)
=(x2+x+1) [x(x-1)+2012]
=(x2+x+1) (x2-x+2012)
Phân tích các đa thức sau thành nhân tử
a) (x+y+z)^3 - x^3 - y^3 - z^3
b) x^4 + 2012x^2 + 2011x + 2012
![](https://rs.olm.vn/images/avt/0.png?1311)
= x3 + y3 + z3 + 3x2yz + 3xy2z + 3xyz2 - x3 -y3 - z3
=3x2yz + 3xy2z + 3xyz2
= 3xyz( x + y + z)
b.
x^4+2012x^2+2012x-x+2012=
(x^4-x)+2012(x^2+x+1)=
x(x-1)(x^2+x+1)+2012(x^2+x+1)=
(x+2012)(x^2+x+1)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(\left(x+y+z\right)^3-x^3-y^3-z^3\)
\(=\left[\left(x+y\right)+z\right]^3-x^3-y^3-z^3\)
\(=\left[\left(x+y\right)^3+z^3+3.\left(x+y\right).z.\left(x+y+z\right)\right]-x^3-y^3-z^3\)
\(=\left[x^3+y^3+3xy.\left(x+y\right)+z^3+3\left(x+y\right).z.\left(x+y+z\right)\right]-x^3-y^3-z^3\)
\(=3xy\left(x+y\right)+3\left(x+y\right)z.\left(x+y+z\right)\)
\(=3.\left(x+y\right)\left(xy+zx+zy+z^2\right)\)
\(=3.\left(x+y\right)\left(y+z\right)\left(z+x\right)\)
b) \(x^4+2012x^2+2011x+2012\)
\(=x^4-x+2012x^2+2012x+2012\)
\(=x.\left(x^3-1\right)+2012.\left(x^2+x+1\right)\)
\(=x.\left(x-1\right)\left(x^2+x+1\right)+2012.\left(x^2+x+1\right)\)
\(=\left(x^2+x+1\right)\left(x^2-x+2012\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(a\text{)}\left(x+y+z\right)^3-x^3-y^3-z^3\)
\(=\left(x+y+z-x\right)\left[\left(x+y+z\right)^2+x\left(x+y+z\right)+x^2\right]-\left(y^3+z^3\right)\)
\(=\left(y+z\right)\left(3x^2+y^2+z^2+3xy+3xz+2yz\right)-\left(y+z\right)\left(y^2-yz+z^2\right)\)
\(=\left(y+z\right)\left(3x^2+y^2+z^2+3xy+3xz+2yz-y^2+yz-z^2\right)\)
\(=\left(y+z\right)\left(3x^2+3xy+3yz+3xz\right)\)
\(=3\left(y+z\right)\left(x^2+xy+yz+xz\right)\)
\(=3\left(y+z\right)\left(x+y\right)\left(x+z\right)\)
\(b\text{)}x^4+2012x^2+2011x+2012\)
\(=\left(x^4-x\right)+\left(2012x^2+2012x+2012\right)\)
\(=x\left(x^3-1\right)+2012\left(x^2+x+1\right)\)
\(=x\left(x-1\right)\left(x^2+x+1\right)+2012\left(x^2+x+1\right)\)
\(=\left(x^2-x\right)\left(x^2+x+1\right)+2012\left(x^2+x+1\right)\)
\(=\left(x^2-x+2012\right)\left(x^2+x+1\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
x4+2012x2+2012x+2012
=(x4-x)+(2012x2+2012x+2012)
=x(x3-1)+2012(x2+x+1)
=x(x-1) (x2+x+1) + 2012 (x2+x+1)
=(x2+x+1) [x(x-1)+2012]
=(x2+x+1) (x2-x+2012)
![](https://rs.olm.vn/images/avt/0.png?1311)
x4+2011x2+2010x+2011
=(x4+x3+x2)+(2011x2+2011x+2011)-(x3+x2+x)
=x2(x2+x+1)+2011(x2+x+1)-x(x2+x+1)
=(x2+x+1)(x2+2011-x)
x4+2011x2+2010x+2011=x4-x+2011x2+2011x+2011
=x(x3-1)+2011(x2+x+1)
=x(x- 1)(x2+x+1)+2011(x2+x+1)
=(x2+x+1)[x(x-1)+2011]
=(x2+x+1)(x2-x+2011)
![](https://rs.olm.vn/images/avt/0.png?1311)
=(x4−x3+2011x2)+
(x3−x2+2011x)+(x2−x+2011)
=x2(x2−x+2011)+x(x2−x+2011)+(x2−x+2011)
=(x2+x+1)(x2−x+2011)
=(x4−x3+2011x2)+(x3−x2+2011x)+(x2−x+2011)
=x2(x2−x+2011)+x(x2−x+2011)+(x2−x+2011)
=(x2+x+1)(x2−x+2011)
x3−x2+2011x)+(x2−x+2011)
=x2(x2−x+2011)+x(x2−x+2011)+(x2−x+2011)=(x2+x+1)(x2−x+2011)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(A=\left(x+1\right)\left(x+2\right)\left(x+3\right)\left(x+4\right)-20\)
\(=\left(x^2+5x+4\right)\cdot\left(x^2+5x+6\right)-20\)
Đặt: \(x^2+5x+5=a\)Khi đó ta có:
\(A=\left(a-1\right)\left(a+1\right)-20=a^2-21=\left(a-\sqrt{21}\right)\left(a+\sqrt{21}\right)\)
tự thay trở lại
1) \(\left(x^2+3x+1\right)^2-1=\left(x^2+3x\right)\left(x^2+3x+2\right)=x\left(x+3\right)\left[\left(x^2+2x\right)+\left(x+2\right)\right]\)
\(=x\left(x+3\right)\left[x\left(x+2\right)+\left(x+2\right)\right]=x\left(x+3\right)\left(x+1\right)\left(x+2\right)\)
2) \(x^4+2012x^2+2011x+2012\)
\(=\left(x^4-x\right)+\left(2012x^2+2012x+2012\right)\)
\(=x\left(x^3-1\right)+2012\left(x^2+x+1\right)\)
\(=x\left(x-1\right)\left(x^2+x+1\right)+2012\left(x^2+x+1\right)\)
\(=\left(x^2+x+1\right)\left[x\left(x-1\right)+2012\right]\)
\(=\left(x^2+x+1\right)\left(x^2-x+2012\right)\)